The present invention relates to a disc brake device, and particularly relates to an improvement in a disc brake device in which the anchoring property of friction pads is improved.
A conventional disc brake device has a structure in which a pair of friction pads are provided on opposite sides of a brake disc and held slidably in an axial direction of the disc by a support member secured to a stationary portion of a vehicle. The friction pads are pressed by a hydraulic actuator into frictional engagement with the disc to thereby obtain braking force. In the disc brake device of this kind, it is necessary that the braking force generated by the friction pads when the friction pads pressingly sandwich the disc is effectively and dispersedly transmitted to the support member. Accordingly, as shown in FIG. 4, U.S. Pat. No. 4,915,198 discloses a disc brake device having a structure in which each of friction pads is of a sectorial shape so as to form slant side surfaces extending substantially along the radial direction of the disc, the center of the inner circumferential portion of the friction pad is cut out so as to form stepped engaging portions opposed to each other, and on the other hand, the support member is provided with anchor portions for receiving the slant side surfaces respectively and anchor portions for receiving the stepped engaging portions respectively. In such a structure, the braking force causes the slant side surfaces of the friction pads to abut onto the corresponding anchor portions at the disc run-out side, while it causes the stepped engaging portions of the friction pads to engage with the anchor portions at the disc run-in and disc inner-circumferential side, so that the braking force is dispersedly transmitted to the support member. Accordingly, the transforming action of the support member is suppressed.
In the above configuration, because the moment for causing the friction pads to rotate along the disc surface in braking is generated, a structure in which the outer circumferential edges of the friction pads are pressingly supported by spring members or the like is employed as disclosed in EP No. 352559 (corresponding to U.S. Ser. No. 07/378101). In the structure, anchoring clips preferably made of a rust preventing material are generally provided on anchor portions for preventing wear so that the outer circumferential end edges of the friction pads are pressed toward the center of the disc both at the disc run-in and run-out sides thereof.
In the conventional disc brake device, however, the pressing forces caused by the anchoring clips so as to press the friction pads from their outer edges are set so as to be equal both at the disc run-in and run-out sides thereof. Accordingly, in the not-braking state, the urging load P.sub.i at the disc run-in side and the load P.sub.o at the disc run-out side are exit side are equal to each other, so that clearances A and B between the inner circumferential stepped engaging portions of the friction pad and the anchor portions of the support member are equal to each other.
However, at the time of the braking, each friction pad moves until the clearance A at the disc run-in side becomes zero, and the pushing-up force C is generated along the radial direction of the disc at the disc run-in side. Accordingly, there have been problems in that the friction pad is in an unstable state until it closely contacts with one of the anchor portions which receive the braking force, so that noises are generated and uneven wear of the lining due to irregular movement of the friction pad occurs.